what is the purpose of registering the hashkey on facebokk app page

Sorry if this a stupid ques开发者_运维知识库tion but really want to know what is the purpose of registering the hashkey on facebokk app page. I nowhere use it in my application(if we have to use it then please let me know where).

The question is How my app will be authenticated using hashkey?? And how to sign my app using hash key??? Thanks for your Help!!!

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Facebook requires an additional layer of security for mobile apps in the form of an 
application signature. You need to put your Android application signature into your 
Facebook application settings. You can generate a signature by running the keytool that 
comes with the Android SDK. The following shows how to export the key for your app using 
the debug defaults specified by the Android SDK and Eclipse.

Also Check this Hash Key for Single Sign-On

Also if i put another Key Hash which is not generated by me

You will get Invalid key Error if you use Wrong Key Hash .

Check this Login failed for Invalid Key

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It's used as another layer of security. On how much it's actually used, I'm not 100% sure. But, here's a few links that might help.

Use of the Facebook App Key Hash

https://developers.facebook.com/docs/mobile/android/build/#sig